Magnetron



y 29, 1952 H. J. REICH 2,605,445

MAGNETRON Filed May a, 1947 2 Sl-IEETSSl-IEET 1 2 Fl. 2A

in i

INVENTOR. FIG. I HERBERT J. REICH ATTORNEY July 29, 1952 I H 2,605,445

' MAGNETRON Filed May 8, 1947 2 SI-lEETSSl-IEET 2 INVENTOR. HERBERT J. REICH BY W ATTORNEY Patented July 29, 1952 MAGNETRON Herbert J. Reich, New Haven, Conn, assignor, by mesne assignments, to the United States of America as represented by the. Secretary of the Navy Application May 8, 1947, Serial No. 746,775

13 Claims. I

The present invention relates to generators of ultra-high-frequency electromagnetic energy, and more particularly, the invention is concerned with tunable-resonator electron-discharge apparatus operable at frequencies of or more cycles per second.

Ultra-high-frequency wave-energy generators are known which consist of a cylindrical cathode, a segmented or slotted anode coaxially disposed around the cathode, and a plurality of hollow cavity resonators connected to the anode at the slots therein. Electrons produced at the cathode are caused to gyrate or move spirally about the cathode in a cathode-anode interaction space by means of an axial magnetic field provided by a magnet whose poles are in axial alignment with the cathode and a radial electric field maintained between the cathode and anode. By proper selection of the voltage of the radial electric field and of the intensity of the axial magnetic field, the whirling electrons may be caused to yield energy to set up and reenforce standing electromagnetic waves in the resonators. Such generators, known in the art as cavity-resonator magnetrons, are efl'icient generators of electromagnetic energy at ultra-high frequencies largely determined by the fundamental frequency of the resonators as excited in a predetermined desired mode of oscillation.

Difliculty is encountered in the operation of such magnetrons where variation in operating frequency is desired or necessary. Known methods of controllably varying the operating frequency are productive of but small tuning ranges, and generally, even such small tuning ranges are accomplished at the expense of the overall Q of the apparatus with consequent reduction of the efficiency of the apparatus.

Accordingly, it is a principal object of the present invention to provide novel apparatus for generating ultra-high-frequency radio energy, particularly for frequencies of 10 or more cycles per second.

Another object is to provide novel ultra-highfrequency energy generator apparatus that is tunable over a relatively wide band of frequencies with substantially no alteration of the Q of the apparatus.

Still another object is to provide novel electrical and mechanical arrangements, including the structures as a whole, means for accomplishing adjustments of the high-frequency resonant circuits utilized therein, and means for the accomplishment of other desirable functions within the scope of the invention, including frequency variation and stabilization, andother functional operations desirable in M connection with the generation of high-frequency oscillations. a

According to a preferred'embodiment of. the invention, wideband tuning of a magnetron" is accomplished by'providing a plurality of resonator devices in the form of adjustable-length, resonant sections of coaxial line, each of said resonant sections being individually adjustable, and means for conjointly adjusting the lengths of all the sections, whereby a range of tuning is provided for the magnetron that is substantially greater than that provided by prior art magnetron generators. t 1 Other objects and advantages willbecome apparent from the specification; taken in connection. with the accompanying drawing wherein the invention is embodied in concrete form.

In the drawing: Fig. 1 is a side elevational view, partly in crosssection, of a preferred embodiment of the invention, I Fig. 2 is a cross-sectional viewtaken along. the line 2-2 of Fig. 1, 1

Fig. 2a is-a fragmentary, view illustrative ofga detail of construction, Fig. 3 is a transverse cross-sectional viewillustrating a modified form ofgthe invention, Fig. 4 is a fragmentary elevational View; partly broken away, showing another modification, and Fig. 5 is another fragmentary elevational view, partly broken away, illustrative of-still another modified form of the invention. 4 Figs. 1 and 2 disclose a-magnetron in accordance with the present invention. As shown, the magnetron comprises a cylindrical shell I l which serves jointly as the evacuated envelope and anode of the magnetron and'comprises a side wall l3 and endwalls-l5, ll. One endwall; lflais preferably removable to provide access to,-;the interior of the shell II- and, before evacuation, wall ll may be secured in any suitable ,manner, as by silver soldering, to provide a vacuum-tight closure for the shell. 7 Coaxially mounted within the shell l-l is aconventional cathode assembly l9 consisting of an electron emitter 2| such as an activated oxide surface heated by. afilament 2,3: (Fish -'2) which is, in turn, connected by means-of .leads; 25 2. suitable source of drivingand .heating' potential ,(not shown). The filament and cathode may be conductively connected for operation at the same direct potential.

: m u n -re at Oath? h ifl s a wall I3 is provided with a plurality of apertures equally spaced around the periphery of shell ll and in a transverse plane midway between end walls l5, l1. Coaxial-line L-fittings 21 are mounted in the apertures, each said fitting comprising a tubular outer conductor 29 and an inner conductor. rod 31 coaxially supported within the outer conductor 29'by, means of dielectric beads or spacers 33. The fittings 21 are suitably secured in the wall [3, as by brazing or silver soldering, or any other suitable means for ensuring a vacuum-tight joint. The vacuum system is made complete by making the-bead 33 nearer the wall [3 a vacuum seal, thepar s of the apparatus beyond this bead being: in communication with the atmosphere, if desired.

The inner end of the inner conductor-3| projects into the interior of shell H and may be terminated in a loop 35 for coupling to the-electromagnetic field which may exist in the interactionspacebetween cathode wand a de' say beefiectediniany desired manner,

a as; by'means of fins 36.

In the illustrative embodiment, there are shown eight apertures in the anode wall I3, seven *of: which are provided with L-fittings 21 as de scribed. The eighthtaperture is provided with .a conventional coaxial line output terminal'or antenna seal 31, for coupling the-magnetron: to a .u'sefulrload. It will .be understood that the number of L-fittings 'heredisclosed is merely illustrative, any other suitable number may be employed.

Adjustable-length sections 39 of coaxial izline are utilized as resonators and,.as shown; theresonatorsiareadaptedto be'deta'chably coupled to the L fittings 21 by. a .conventional coupling-nut 'ara-ngem'ent; iAs shownzinFig. 1, the adjustablelength resonator sections 39 are of identical construction, each being formed of a pair of ;.tele- -scopingly adjustable portions 41,143 01 coaxial -'line,' said portions having outer conductors 45,

slot to receive the slightly tapered end of the inner conductor 3| of'the L-fitting. Asis well known, the inner conductor 45 may be suitably positioned coaxially of the outer conductor45 by means of suitably positioned dielectric beads-33. -A' short-circuiting conductive disc 53 I is ri idly "connected between inner c0nduct0r-5l and outer conductor of resonator portion-43 so that, by

adjustably varying the degree of insertion-:of

portion 43 iii-resonator portion -4l,-the effective electricallength of resonator'39 maybe altered.

I (.a'renerally', the eifective electrical length is preliminarily adjusted to be substantially one-half wavelength at thedesired operating frequency of the magnetron.

Each of the other L-fittings'Z'l are adapted to be provided with adjustable-length coaxial'dine resonators-39 similar" to that described herein- -above. Only one other-resonator 33 is shown in 'fFig. l, the other adjustable-length coaxial line -resonatorshaving-been omitted from the drawingin the interestof' clarity ofdisclosure.

' Tq provide forconjoint adjustment of the electrical lengths of resonators -39 there "is provided an apertured interconnecting disc 55,

' through the holesof which the free ends'of' the resonators 39 are adapted to be passed. Any suitable means may be used to provide for detachable mechanical connection of the resonators and the disc 55. For example, washers 51 may be secured adjacent the free ends of the portions 43 to provide shoulders on which the interconnecting disc 55 :my rest. -A series of aligned apertures 59 (Fig. 2a) may be formed in the outer conductor 41 of the portion 43 through which a pin 61 may be passed to secure the disc 55 in position. It will be noted that the series of aligned apertures are provided to make possible the addition of one or more additional removable washcrs of suitable thickness to compensate for inequalityinthe structural lengths of the coaxial line resonators 39 that may result from a preliminary. independent adjustment of the electrical length of the individual resonators. A

control rod 63 is centrally mounted on and secured to the disc 55, and may be provided with aknob $5 for manual adjustment of the disc 45,01, the rod 53 may-be connected mechanically to any other suitable source of motive means for tronssweeping across the resonatorstil isto initiate and sustain ultra-high-frequency electromagnetic oscillations Within theresonators in a manner similar to the production of ultra-high-frequency electromagnetic oscillations in th hollow cavity resonators of prior-known types of magnetrons. Accepted theories of the mechanism whereby this operationisachieved are set forth in an article by J. B. Fisk, H. D. I-Iagstrum and P. L. Hartman in The Bell System Technical Journal, vol.-XXV,.1946, pages169-221, to which reference is made for a fuller description.

As notedabove, th frequency ofoscillation of the-magnetron is largely determined byfundamental frequency of the resonators, which, in

turn, is determined by the effective electrical length thereof. Thus the'lengths of the resonators maybe independently and/ or conjointly adjusted so that the electrical'lengths are equal to one-half wave length at the desired operating frequency. It will be understood that electrical lengths corresponding to integral multiples of one-half wavelength may also be utilized. 7

The operating'frequency of the magnetron is thus rendered easily variableover a Wide range of frequency values. Such variations are accomplished'by merelychanging th effective lengths of the resonatorsby moving theinterconnecting disc 55 in the appropriate direction. a

Frequency modulation of the -magnetron may also easily be accomplished, as :by-mechanicaHy coupling the disc55 to any suitable motive. means for alternately increasing and decreasing the, effective lengths. of the resonators, as desired.

The ultra-high-frequency energy 'generatedin the magnetron may beidelivered to any. useful load or utilization device by means of the couplingloop full complement of L-fittings 21 is provided hereir'n each fitting being adapted to couple acoaxial line resonator (not shown) to the interaction space between cathode l9 and anode 13" of the type and in substantiallythe same manner asset forthabove. One or more'outp'ut couplings 61, '69.

may be mounted with the loopsthereof oriented in the interaction space so that the magnetic flux lines from the resonators thread therethrough in any desired amounts In this manner it will be seen that multiple outputs are readily available.

To obtain greater uniformity of electromagnetic-field distribution relative to the cathode the modification shown in Fig. 4 is proposed. As

shown; two circular arrays H, 13 of reson'atorcoupling L-fitting's are provided. Resonators (not shown) of the type described in connection with Figs. 1-2 are adapted to be coupled, as above,

to respective ones of the L-fittings of each array' As shown in Fig. 4, the L-fittings of each array 7 i, 13 are disposed in concentric, axially-displaced circular arrangements with respective onesof the fittings 75 in array H in axial alignment with respective ones of the fittings 11 of the array 73.

The fittings l! of array 13 are preferably formed with horizontally extending portions 79 sufliciently longer than the corresponding portions of fittings 75 of array H so that the axes of the resonators of each array, when assembled, are disposed along coaxial cylinders of unequal diameters. Conjoint variation of the electrical lengths of the resonators of each array may be accomplished by means of an interconnecting disc (not shown) in a manner similar to that shown above. i 1

It will be seen that the dielectric spacer 33 that provides a vacuum seal between the shell wall 43 and theexterior may be positioned at the-end of the L-fittings I5 and 11 inasmuch as the points of insertion of the L-fittings are adjacent to voltage nodes.

Output couplings 8!, 83 for delivering the ultrahigh-frequency energy generated in th magnetron to utilization devices are provided in a common transverse plane symmetrically disposed between arrays H, 73, and, as shown, the couplings 8|, 83 may be staggered between adjacent pairs of vertically-disposed resonators.

Fig. 5 shows a further modification of the invcntion, which While generally similar to the form illustrated in Fig. 3 insofar as the resonator arrangement is concerned, differing therefrom in that the output couplings 85, 81 are provided in a common plane displaced from the medial plane occupied by the fittings 21. In this form, the output couplings 85, 81 are preferably disposed in axial alignment with the resonators.

There has thus been described in the foregoing specification a magnetron generator wherein wideband tuning is accomplished by means of adjustable-length resonant sections of coaxial line, with each of the sections being independently adjustable and conjointly adjustable, as desired.

- 'Itis tobe understood that various modifications and changes may be made in this invention without departing from. the spirit and' scope thereof .as set forth in the appended claims,

I l f i. i

1." A high-frequency tube structure comprising means defining a substantially homogeneous cylindrical conductive shell adapted to contain; a rotating electromagnetic field therewithin', cathode means disposed axiallyof said shell for producing asupply of electrons, means adjacent said shell f or forming a plurality of beams of electrons rotating in synchronism with said field? and definingpaths substantially radial of saidl shell, and a plurality of short-circuited sections of coaxial I transmission line extending out-- wardly from said shell and coupled in energyinterchanging relation with the interior of'saidi shell, said sections of line forming the sole princi'pal' frequency-determining elements of the tube structure.

2. A high-frequency tube structure comprisin means defining a substantially homogeneous cylindrical conductive shell, cathode means dis posed axially of said shell for producing a supply" of electrons, means adjacent said shell for form-- ing a plurality of rotating beams of. electrons;

defining paths substantially radial of .said shell,v a plurality of short-circuited sections of coaxial? transmission line of adjustable length andex tending outwardly. from said shell andcoupled in energy-interchanging relation with the interior of said shell, said sections forming the sole? principal .frequencyedetermining elements of the tube structure, and means for conjointly varying the lengths of said sections.

3. A high frequency tube structure comprising a cylindrical shell, means for producing arotating space charge of electrons extending substantially radially of said shell, a plurality of sections of coaxial transmission line disposed about and projecting radially from said shell, means in said shell for coupling said sections to said rotating space charge, ,whereby ultra-high-frequency electromagnetic fields. are induced in said trans' mission line sections, and coaxial-line means connected to 'each said section for conjolntly adjusting the lengths ofsaid sections. thereby to alter the frequency oi oscillation of said'ultrahigh-frequency fields.

4. A high-frequency tube structure comprising a cylindrical shell, means for producing a rotatingspace charge of electrons extending substantially radially of said shell, a plurality of spaced .arrays of coaxial transmission line sections, each 5. In apparatus of the kind described, means defining an electron beam oscillating field interaction space, means for producing a copious supply of electrons within said space, means for causing rotational motion of said electrons as a plurality of wheel-like spokes, a plurality of coaxial transmission line sections, each said section having respective ends thereof circumferentially diseased in a; common planein Said spac a axialline sections ion-short-circuiting the. co-

axial lines, whereby. each, saidsection forms. a resonator wherein. standing, electromagnetic waves of a. predetermined frequency are .initiated, and means interconnecting .said adjustable 'means forconjointly varying the. position. of said short-circuiting. means thereby to vary. the fre; quency of said, resonators.

6. An electron-discharge,device.comprising, an

anode consisting essentially. of a cy indrical memberhaving. a plurality'of, openings in the wall thereof, asectionof. coaxial transmission linev fitted in each said opening, said; sections .beingiof predetermined, length to resonate at, substantially the frequency of the ultra-high-frequency energy to, begenerated by said device and... adapted toprovide, the sole principal 'frequency-determining elements of the deyicaa cathode within said member for, supplying electrons withinsaid cylindrical'member, and means adjacent said cathodefor providing a magnetic field within said member between. said anode and cathode. and tolwhich said electrons are subi cted. I

.7 electron discharge device comprising an anode consisting, essentially of a cylindrical member having a plurality of, openings inthe wall thereof, a section of coaxial transmission line fitted ineach said opening, said sections being of'predeterminedlength to resonate at substantially the frequencyto be generated by said device, a cathode within said; member-for supplyin t electrons within said. cylindrical member, means adjacent said-cathode for providing a magnetic field within said memberandbetween saidanode and cathode and to. which saidelectrons arev subjected, and, interconnecting said sections .for simultaneously altering the predetermined lengths of L said sections of coaxial line to rendersaid sections resonant at another frequency thereby to alter. the frequency of" the energy generator by .said device. H I

8, Electrical dischargedevice of the magnetron type, comprising an evacuated cylindrical conductive shell, means for producing a copious supply of electrons within said shell, means for causing rotational motion of said electrons, a plurality of independently adjustable coaxial transmission-line sections disposed to interact with said rotating electronsthereby to set up a rotating electromagnetic field withinsaidshell, each said section. being dimensioned to form a resonator wherein standing electromagnetic waves of a predetermined frequency are set up, and; multiple-channel means projecting into said shell and extending to the exterior thereof for conducting energy from said apparatus to a utilization device.

9;'A high-frequency tube structure of the magnetron type, comprising a cylindricalganode shell, means supported axially of said shell for cloud 8 producing. rotating beams of electrons. generally defining paths radial of said,sh'el1, spaced ultrahigh-frequency resonators extending radially and outwardly from said shell, said resonators comprising sections of coaxial transmission line,

tivelojops at the ends of said sections of, trans,-

mission line, said loops being disposed within the reactionspace insaid shell and. in mutual. en.- ergy-coupling relation with said rotatingibeams. 11. VA magnetron. tube structure comprising a substantiallyjhollow cylindrical .anode, means partly within said. anodefor producing a rotating of electrons extending substantially radially of, said anode, a plurality of sectionsof coaxial transmission line dimensioned for resonance at the operating frequency of said tube structurev and disposed about and projecting radially from said anode, said sections forming substantially the sole "frequency-determining element of the tubestructure, and means coupling said sections to saidrotating electron cloud, whereby ultrahigh-frequency electromagnetic fields are 1 induced in said transmission line sections.

12. The tube structure as claimed in claim 11 wherein said coupling means comprises inductive loops at the ends of saidsections of transmission line and disposed within the reaction space in said anode, said loops being at voltage nodes of the oscillating fields in said sections.

13. In a high-frequency magnetron device, having a cylindrical anode surface, and a plurality of coaxial-line resonators projecting radially therefrom, and in which the anode surface and the resonators are intercoupled by a rotating high frequency electromagnetic field in a region adjacent the resonators, extensions on said coaxial-line resonators, said extensions being arranged in mutually parallel relation and. parallel to the axis of said anode surface, movable tuning means in said extensions and including adjustable short-circuited sections of coaxial transmission line telescopically fitted in each said coaxial line resonators, and means for con jointly moving said shortv-circuited sections.

RT REICH,

REFERENGES CITED The. following references are of record in the file of this patent:

UNITED STATES PATENTS 

